The development of the next generation of wireless mobile communications for 5G cellular communication is underway. With spectrum always being at a premium, engineers are turning to millimeter wave frequencies to provide those next generation services.
However, while the above spectrum is presently unused and can be used to realise multi-gigabit wireless communications, it is well-known within the art that electromagnetic waves at these frequencies suffer from high attenuation and high path loss, which, consequently, limits the cell sizes that can be realised.
Various techniques exist for addressing the path loss, which include using one or more than one diversity technique, such as, for example, spatial diversity/multiplexing, in which two or more different transmit signals are used to increase overall throughput, and beam forming, in which two or more instances of the same signal are used to improve communication reliability.
Nevertheless, millimeter waves present several beam forming technical challenges that comprise, firstly, delay spread and angular spread, which are particularly problematical under Non-Line Of Sight (NLOS) conditions such as found indoors, and, secondly, beam misalignment, which arises when channel state information or beam tracking is inaccurate due to, for example, at least one or more of measurement errors and user equipment mobility.